Digital displays are widely used in a number of devices, including televisions and portable devices such as mobile phones, notebook computers, and tablet computers. Some digital displays, such as three-dimensional (3D) digital displays, incorporate special combinations of panels to allow them to produce particular visual effects to a viewer. For example, in a 3D digital display, a barrier panel (also known as a parallax barrier) is aligned with and in overlying relationship with a thin-film transistor (TFT) panel of the display. The barrier panel contains an exposure pattern comprising a plurality of slits or a lattice of apertures to allow selective exposure of the underlying TFT panel. At a given viewing angle, a viewer's left eye will see light emitted by different pixels differently from the right eye, thus producing an autostereoscopic effect to the viewer.
In order for the stereoscopic effect to work as desired, it is necessary to precisely align the barrier panel with the TFT panel prior to lamination.
Traditionally, alignment of the digital display panels requires that a backlight unit of the display be lit up, or that special alignment patterns be applied to borders of both the TFT panel and the barrier panel, or be displayed on the TFT panel.
For example, PCT publication WO2007/083925 discloses a method for attaching a display panel for a stereoscopic image. A stereoscopic camera (double camera) system is used to simulate the human visual system (the two cameras representing the left and right eyes respectively). A stereoscopic image composed of interlaced left eye and right eye images is displayed on a stereoscopic panel which overlaps with a backlit display module, the backlighting being turned on. The cameras record the stereoscopic image and the relative positions of the stereoscopic panel and display module are adjusted until the left and right eye images are distinguishable in the respective cameras. A disadvantage of this method is that the display panel needs to be electrically connected and powered on in order to perform the alignment and panel attachment. Requiring the display panel to be powered on makes it difficult, if not impossible, to fully automate the assembly process. A further disadvantage is that it requires a relatively complex setup.
A disadvantage of known methods which use alignment marks is that marks must be applied to both the TFT panel and the barrier panel. 3D display manufacturers typically perform customization of the barrier panel, but use off-the-shelf TFT panels. Although it is generally straightforward to incorporate alignment marks during barrier panel customization, it is not feasible (technically or economically) for 3D display manufacturers to add alignment marks to the TFT panel itself.
There remains a need for a method which allows 3D display manufacturers to achieve alignment of barrier panels with readily available off-the-shelf TFT panels, without needing to customize the TFT panels. There also remains a need to achieve such alignment without needing to provide power to the TFT panel during the alignment process.